1. Field of the Invention
The present invention relates to a polychloroprene latex, a polychloroprene latex composition, and a molded article. More specifically, it relates to a polychloroprene latex for use in dip molding, a composition containing the latex and various additives, and an article dip-molded therefrom.
2. Description of the Related Art
Polychloroprene latexes, which are superior in many properties including mechanical strength, weather resistance, heat resistance, and chemical resistance, have been used in various fields including dip-molded articles, textile-processing agents, paper-coating agents, adhesive agents, bonding agents, elastic asphalts (modified asphalts), and elasticity cements. In particular in the field of dip-molded articles, polychloroprene latexes have been used as a primary raw material for various gloves including household, industrial and surgical gloves.
Generally a method, so-called coagulant solution method, has been used in dip molding. In the coagulant solution method, a 3D-shaped dip-molding ceramic or metal mold carrying a coagulant solution having an action to coagulate polychloroprene latex coated on the surface thereof is dipped into and withdrawn from a polychloroprene latex composition containing sulfur, vulcanization accelerators, and others, to give a film coated on the surface. Separation of the film obtained from the dip-molding mold gives a product in a particular shape.
In the coagulant solution method, in order to form a uniform and smooth film on the surface of the dip-molding mold, it is needed to increase the coagulability of the polychloroprene latex by the coagulant. It is known that the amount of the emulsifier used in the polychloroprene latex is preferably lowered as much as possible to improve the coagulability thereof. However, reduction of the emulsifier content may leads to deterioration in anti-freezing stability of the polychloroprene latex, making it impossible to use the latex as the raw material in dip molding because of increased viscosity and freezing.
For the reasons above, there exists a demand for a method of increasing the coagulability of the polychloroprene latex used in dip molding, while preserving the anti-freezing stability thereof. Thus, addition of some emulsifiers to the polychloroprene latex was studied for improvement of the anti-freezing stability. For example, proposed was a method of producing a polychloroprene latex superior in freezing resistance and anti-freezing stability by adding a rosin acid and a polyoxyalkylene alkyl ether having an HLB (Hydrophile-Lipophile Balance) of 10 to 17 (see Patent Document 1).
Also proposed was a method of adding an alkali metal carboxylate salt and a nonionic emulsifier having a polyoxyalkylene structure containing branched alkyl chains having 9 to 16 carbon atoms and having an HLB of 9 to 16 (see Patent Documents 2 and 3). The method of producing a chloroprene latex described in Patent Documents 2 and 3 gives a polychloroprene latex that is not frozen even at −3 to −7° C. Also proposed was a method of producing a polychloroprene latex superior in chemical and mechanical stabilities by emulsion polymerization of chloroprene monomers in the presence of a polyoxyethylene alkyl ether having an HLB of 14 to 19 and a polyvinyl alcohol (see Patent Document 4).